config.generators.api_only = true set rails api option on generators

railties/lib/rails/generators.rb

@@ -105,6 +105,10 @@ def self.fallbacks
 
     def self.api_only!
       hide_namespaces "assets", "helper", "css", "js"
+
+      options[:rails].merge!(
+        api: true
+      )
     end
 
     # Remove the color from output.

railties/test/application/generators_test.rb

@@ -126,7 +126,7 @@ def with_bare_config
       end
     end
 
-    test "api only generators hide assets, helper, js and css namespaces" do
+    test "api only generators hide assets, helper, js and css namespaces and set api option" do
       add_to_config <<-RUBY
         config.generators.api_only = true
       RUBY
@@ -139,6 +139,7 @@ def with_bare_config
       assert Rails::Generators.hidden_namespaces.include?("helper")
       assert Rails::Generators.hidden_namespaces.include?("js")
       assert Rails::Generators.hidden_namespaces.include?("css")
+      assert Rails::Generators.options[:rails][:api]
     end
   end
 end